1. Field of the Invention
The present invention relates to the field of physical document management and, in particular, to systems and methods for preserving and maintaining the integrity of printed documents.
2. Description of Related Art
Electronic documents, such as those created using many document and/or word processing applications, generally have several layers of data. Each layer in the document, termed a “document layer,” contains some information related to the document or its contents. For example, the text seen by an end user creating, editing, or viewing a document may be represented in one layer of a document. Another layer may contain some of the drawings and/or figures that are part of the document. Finally, a third layer may contain the background over which the text and drawings are displayed. One of the advantages of organizing documents in layers is that each layer may be edited and/or created separately from other layers in the document. Thus, a layer may be changed without requiring any change in other layers associated with the document.
In addition to the layers described in the example above, a document may also contain “invisible layers.” These invisible layers may contain data pertaining to the document or its contents rather than actual document content that is seen by users. Such data is also often called meta-data. An invisible layer may include, for example, information about people who have edited or viewed any part of the document. Another invisible layer may contain indexing information such as terms that occur frequently in the document. Users editing or viewing the document do not normally see invisible layers. Menus provided by the document processing software may allow a user to explicitly request the information contained in an invisible layer in order to view the contents of that layer.
Invisible document layers may also be used by other applications or the operating system to enforce policies concerning the document. These policies may restrict the people who have access to the document or may prevent applications or users from making changes to portions of the document. Document layers may also be used to authenticate and ensure the integrity of a document. For example, an invisible document layer may contain a digital signature that can be used to establish that an electronic version of a document originated with the entity associated with the digital signature and that no changes were made to the document after it was digitally signed.
Although invisible layer data can be used electronically, for example, to authenticate the content of a document and protect against alteration while it is in electronic form, such protection ceases when the document is printed. Printed documents contain only the actual content of a document, and data stored in document layers is lost. Thus, once a document has been printed, a recipient has no way of determining where the document originated, or where it is stored, or whether the document was altered, even though such information may have been available in document layers.
Preservation of layer data in printed documents would allow recipients of a printed document to automatically recreate preserved layer data, associate the preserved layer data with a document's contents, and facilitate the enforcement and maintenance of policies associated with the printed document.